The present disclosure relates to a modular battery system. To be more precise, the disclosure relates to a battery system which has a battery with a plurality of battery modules which can be selectively activated or deactivated by means of actuation, wherein, in the activated state, the battery module voltage of a respective battery module contributes to an output voltage of the battery and, in the deactivated state, the battery module is uncoupled from the current path of the battery. The disclosure also relates to an associated method for charging battery modules and to a method for balancing battery modules. The disclosure also relates to a motor vehicle having the battery system disclosed herein.
It has become apparent that battery systems will be increasingly used both in stationary applications and in vehicles, such as hybrid and electric vehicles, in the future. In order to be able to meet the requirements for voltage and available power given for a respective application, a large number of battery cells are connected in series. Since the current which is provided by a battery of this kind has to flow through all battery cells and a battery cell can conduct only a limited current, battery cells are often additionally connected in parallel in order to increase the maximum current. It is often also advantageous to be able to set the battery voltage in a variable manner, for example in order to match the battery voltage to the operating situation of the motor.
Therefore, earlier patent applications by the applicant have presented battery systems which have one or more battery module lines, it being possible for the individual battery modules of the battery module lines to each be selectively connected and deactivated again in the battery module line. An example of a battery system having a battery module line of this kind is schematically illustrated in FIG. 1. According to FIG. 1, a battery system 100 has a plurality of battery modules 101 which are connected to one another in series and which form the battery module line. Each battery module 101 has one or more battery cells 102, only one of which is illustrated in the drawing for each battery module 101. Furthermore, FIG. 1 explicitly shows only two battery modules 101 but in many applications a battery module line comprises more than two battery modules 101, this being indicated in the drawing by dots. A battery module 101 can comprise any desired number of battery cells 102. According to one embodiment, each battery module 101 can have the same number of battery cells 102, but according to other embodiments one of the battery modules 101 can have a different number of battery cells 102 in comparison to the remainder of the battery modules 101. Each battery module 101 also has two switching elements 103, 104 in each case, wherein a respective battery module can be activated or deactivated depending on the switching position of the switching elements 103, 104. For example, in a switching position in which the switching element 103 of a battery module 101, which switching element is at the top in FIG. 1, is in the closed state, whereas the lower switching element 104 is in the open state, a respective battery module 101 is connected to the battery module line, with the result that the battery module voltage of the respective connected or activated battery module 101 contributes to a battery voltage which is available at the two terminals 105, 106. If, in contrast, the upper switching element 103 is open and the lower switching element 104 is closed according to another switching position, the respective battery module 101 is deactivated. To be more precise, a battery module 101 is uncoupled from the current path of the battery and electrically conductively bridged in the deactivated state, with the result that only the remaining, activated battery modules 101 contribute to the battery voltage and therefore can supply battery current and electrical energy.
One advantage of an arrangement according to FIG. 1 is that a variable, selectable battery voltage can be set in this way. For example, a sinusoidal profile of the battery voltage can be set at the terminals 105, 106 given sufficiently fine division of the battery module line into a plurality of battery modules 101 and given suitable actuation. If, furthermore, a plurality of battery module lines are used, these each being actuated to supply a sinusoidal output voltage, the method can be further correspondingly optimized. For example, three phase-offset sinusoidal voltages can be generated, with the result that a three-phase electric motor can be actuated without an interconnected inverter being required.
However, one disadvantage of a modular arrangement of this kind is that, in order to charge the battery cells 102, suitable confirmation typically also has to be provided by means of the switches 103, 104 which are provided for connecting and bridging purposes, with the result that each of the battery modules 101 is connected into the current path of the battery. To be more precise, in order to charge a battery module 101, for example, from an on-board vehicle electrical system, the respective battery module 101 has to be reconnected if it was previously in the deactivated state. Furthermore, charging of the battery modules 101 is generally possible only from the on-board vehicle electrical system. In FIG. 1, the battery current I is illustrated by the double-headed arrow, wherein the current I flows into the battery cells or is drawn from the battery cells depending on whether the battery is currently charged or discharged. In addition, for the purpose of charging the battery, the energy required for this purpose initially has to be transferred to the on-board vehicle electrical system in order to be able to then charge the cells by connecting the respective modules.